1. Field of the Invention
The present invention relates generally to a solid-state imaging device and a method of manufacturing the same, and more particularly to a solid-state imaging device with a vertical transfer electrode and a method of manufacturing the same.
2. Description of the Related Art
In recent years, attention has been paid to the market of small-sized camera modules which are applicable to digital still cameras and camera-equipped mobile phones. With the reduction in size of camera modules, imaging devices, such as CCDs and CMOS sensors, have been reduced in size year after year. However, since the improvement in sensor performance and the microfabrication are not compatible, it is expected that further microfabrication becomes difficult more and more. A typical example of incompatibility between performance and microfabrication is a decrease in plan-view area of a photodiode. Specifically, although finer microfabrication is made possible by the decrease in plan-view area of the photodiode, the amount of charge that is accumulated in the photodiode decreases. The amount of charge that is accumulated in the photodiode is an important factor which determines the sensor performance, and the decrease in the amount of charge that is accumulated in the photodiode deteriorates the sensor performance. The key to increase the area of the photodiode is finer microfabrication of a component other than the photodiode within one pixel, for instance, finer microfabrication of a transfer gate electrode.
Conventionally, in a solid-state imaging element having a horizontal transfer gate electrode, the transfer gate electrode is formed on the semiconductor substrate via a gate insulation film. A charge accumulation region, a shield layer and a charge transfer destination diffusion layer which receives transferred charge are formed in the semiconductor substrate. The light that has been made incident via a light incidence path is photoelectrically converted in the charge accumulation region to an electric signal. By turning on the transfer gate electrode, the charge that is accumulated in the charge accumulation region is read out to the charge transfer destination diffusion layer via a charge transfer channel. Since the charge transfer channel is horizontal to the substrate surface, this charge transfer is called “horizontal transfer”. The transfer distance of charge is determined by the gate length of the transfer gate electrode. Thus, in order to secure a sufficient modulation degree, a sufficient gate length is necessary, and there is a problem that device microfabrication is difficult. In addition, because of the horizontal transfer, the charge transfer destination diffusion layer needs to be formed on a side opposite to the side of the charge accumulation region of the transfer gate electrode, and there a problem that it is difficult to reduce the plan-view pixel area. Therefore, there has been a demand for a solid-state imaging device and a manufacturing method thereof, which can reduce the pixel area and can secure a sufficient modulation degree.
As related art, there has been developed a solid-state imaging device in which a gate electrode is formed so as to penetrate the substrate, thereby to enhance the efficiency of light incidence in a photoelectric conversion part (see, e.g. Jpn. Pat. Appln. KOKAI Publication No. 2007-96271).